1. Field of the Invention
The technique disclosed in this application relates to a communication device connected to a network, a communication system and a communication control method. Particularly, it relates to server cooperation at the time that a plurality of communication servers perform mutual communication and message conversion processing. Especially, it relates to a communication system to which session control using SIP (Session Initiation Protocol) is applied and a message conversion method in communication systems in which communication systems for providing Web application are connected mutually.
2. Description of Related Art
The 3rd-generation mobile communication system is being standardized so as to aim at providing various multimedia services such as voice, data and animation at high speed and with high quality. The 3GPP (3rd-Generation Partnership Project) advances standardization of “All IP Base Mobile Communication Network” that provides multimedia services such as voice and picture utilizing Internet Protocol (IP) technique on a packet switching network.
The session control system of the All IP Base Mobile Communication Network is named IMS (IP Multimedia Subsystem). The IMS is also adopted in session control technique of NGN (Next-Generation Network).
The SIP (Session Initiation Protocol) is utilized as the session control protocol of the IMS (for example, refer to IETF RFC3261 (2002.6)). The SIP is the protocol for controlling session of IP multimedia communication specified by IETF. The SIP controls establishment, maintenance and disconnection of session among communication devices.
As the representative service using SIP, there is IP telephony service. The IP telephony service is the service for transmitting and receiving voice information through IP network. In the IP telephony service using SIP, virtual speech path or channel (session) is established between communication devices before communication is started. Voice data formed into IP packets is transferred through the established communication path.
Media information such as attributes of voice data is decided upon establishment of session. The communication device notifies the media information using SDP (Session Description Protocol) contained in SIP message. In the SDP, various information concerning session (for example, IP address, port number, kind of media and the like) can be described. As an example of application service using the SIP protocol, there is the third party call control (refer to IETF RFC3725 (2004.6), for example).
Moreover, in order to make it possible to utilize the communication service provided by a communication entrepreneur from Web service, investigation of API (Application Programming Interface) is advanced.
There is the Parlay group as an industrial organization stipulating the API. The Parlay group is deciding on a plan for API named “Parlay X”. The Parlay group cooperates with ETSI (European telecommunication standards institute) and 3rd-generation mobile telecommunication standardization organization (3GPP). The specifications of the Parlay X are issued from the 3 organizations jointly.
The “Parlay X” is API of Web service that does not depend on network and vendor and is not limited to language provided therein for the purpose of use in Web service environment. The “Parlay X” defines open interface abstracted for Web developers but its mounting or implementing method is not prescribed.
In the “Parlay X”, a set of API is stipulated for each service. As service provided using the Parlay X API, there is, for example, 3PCC (3rd Party Call Control) starting 2-party conversation service from Web application (4th Draft ES 202 504-2 Parlay X 3.0 (2007.8)).    Non-patent document 1: IETF RFC3261 (2002.6)    Non-patent document 2: IETF RFC3725 (2004.4)    Non-patent document 3: 4th Draft ES 202 504-2 Parlay X 3.0 (2007.8)